1. Field of the Invention
This invention relates to storage systems, and in particular to storage area networks in which copying and remote copying of data provided by a host is provided.
2. Related Art
Modern storage systems provide users with the capability of continuously sending updates to a primary volume at a primary site and to a secondary volume at a secondary site, that is a mirrored volume of the primary volume, over a network in order to achieve a time-consistent copy of data. The remote copy operation is typically performed by host sending data and write requests to the primary storage system, which acknowledges the receipt of those write requests. Data that arrives at the primary storage system from the host is stored in a cache memory before being written to hard disk drives in the storage system. Either synchronously, by writing the data to hard disk drives, or asynchronously, the data is also written to storage media in a secondary storage system, typically located remotely from the primary storage system. In this manner, highly reliable access to the data is provided, making the system less susceptible to natural disasters or other events which may damage or destroy one of the two storage systems.
In storage networks with 1:1 configurations, satisfying a request for remote copies does not involve special challenges since the consistency of remote copies within the storage subsystems is easy to maintain. The challenges appear when the consistency of the remote copy is intended to be maintained in storage networks that span over multiple storage systems and have N:M configurations. In complex configurations the consistency of remote copies is increasingly difficult to manage. Synchronous remote copy provides a high degree of data currency and integrity, but can operate only at limited distances. In synchronous communications, the sender and receiver need to synchronize with one another before data is sent. This generally limits the communication between sender and receiver to short distances. Synchronous remote copy has a performance deficiency as I/O response times increase with the distance between the primary and secondary sites. This is due to what is known as “propagation delay,” or the fact that, on average, the speed of light takes one nanosecond to travel one foot. This can add up when many miles are involved and synchronous copy techniques are effectively limited to distances of 25 miles or 40 kilometers (10 kilometers for Fibre Channel) depending on performance requirements. TrueCopy asynchronous extension for remote copy is not “real time” like synchronous remote copy, and can operate at any distance and has the data and transaction integrity necessary for disaster recovery. In open systems environments, timestamps from systems timer are used for data synchronization. Utilizing reliable timestamps, along with other information created by the primary system(s), allows systems to transmit updates directly to the secondary system (without any host intervention) and have the secondary system apply the same consistency group algorithms normally provided by a system data mover. This approach allows the enterprise to achieve data integrity in a significantly simpler and less costly hardware-based solution with no impact on server or application performance.
The challenges appear when a consistency group is intended to be set in a system including n primary storage subsystems and m secondary storage subsystems (N:M configurations). In complex configurations it is increasingly difficult to maintain IO consistency in the consistency group.
Nano-copy is a technology that currently provides solutions to the above mentioned problem. The nano-copy technology insures the consistency across multiple storage sub-systems with N:M configuration. Nano-copy technology removes some of the drawbacks of synchronous remote copy (such as maximum distance and data integrity across multiple systems) without the processor-performance overhead usually associated with asynchronous remote copy implementations. Working with TrueCopy asynchronous software, nano-copy technology provides the a nondisruptive, I/O- and time-consistent, long-distance remote copy that can be used safely for disaster recovery and PiT copy. The nano-copy software allows “any-to-any” remote copy, the software providing remote copy with integrity for any number of primary storage systems connected to a single sysplex timer, to any number of remote image systems, anywhere in the world, at any time. Nano-copy technology comes closest to the perfect solution by allowing customers to create a truly nondisruptive PiT copy. A storage-based copy solution creates an image of any amount of data without incurring an application or system outage. Furthermore, the copy can be made to any place on the globe. For disaster protection, nano-copy technology is a product that solves the extraordinarily complex problem of ensuring that critical data can survive a rolling disaster. With outstanding data integrity, nano-copy technology maintains a copy of critical data at any distance, and also does so by using a simple and low-cost technique that has minimal impact on critical applications. Nano-copy technology has the potential for providing solutions to the enterprise. It offers a simple and low-cost alternative to existing remote copy technologies without compromising data integrity. It also provides a capability of taking point-in-time copies without disruption to applications.
What are needed are apparatus and methods of use that allow consistency to be maintained within storage systems with complex configurations without management from a host. One of the main advantages, provided by a capability to maintain consistency within the storage subsystems without the need of external management from a host, is that it provides platform/application independent infrastructure.